OTTAWA - The Harper government quietly introduced strict new security vetting for nominees to Canada's federal spy watchdog after chairman Arthur Porter resigned amid concerns about his business dealings, The Canadian Press has learned.

Appointees to the Security Intelligence Review Committee now must be security cleared to the top-secret level — a rigorous process that wasn't in place when Porter joined in 2008 or became chairman in 2010.

Prior to Porter's resignation in November 2011, potential appointees were subject to only a limited background check — even though review committee members see the most sensitive files held by the Canadian Security Intelligence Service.

The Prime Minister's Office tightened the screening requirements following Porter's abrupt departure, said Adam Green, a spokesman for the committee.

"All of these changes came from that office," he said in an interview.

Former cabinet minister Chuck Strahl, who succeeded Porter as review committee chairman, was the first appointee to the spy watchdog to be screened to the top-secret level in keeping with the new procedures, Green said.

The other two members of the committee were named before the procedures came into effect.

It was five years ago when the Conservatives first appointed Porter — a medical doctor and cancer specialist — to the review committee, which keeps an eye on CSIS and investigates complaints about spy service. He became chairman less than two years later.

Porter, a native of Sierra Leone, quit the review committee after the National Post newspaper revealed he once made a deal — that ultimately fell through — with middleman Ari Ben-Menashe on a $120-million aid-for-development initiative from Russia. It would have given African Infrastructure Group, a firm owned by Porter and his family, the chance to manage infrastructure projects in his homeland.

Ben-Menashe is a controversial figure who has claimed involvement with Israel's spy service. His Montreal consultancy has done work for iron-fisted Zimbabwean leader Robert Mugabe.

Upon his resignation from the review committee, Porter said he was "a proud Canadian and man for whom integrity, honour and respect hold tremendous meaning."

A short time later he stepped down as executive director of the McGill University Health Centre in Montreal. The university is suing him for more than $300,000 — the outstanding balance of a loan and a salary overpayment.

He now runs a private cancer clinic in the Bahamas.

During question period Thursday in the House of Commons, the NDP urged the Conservatives to admit they made a mistake in appointing Porter to the spy watchdog.

Alexandre Boulerice, the NDP's deputy ethics critic, pounced on news of the tougher screening procedures. "If that's not owning up to their mistakes, I don't know what is," he said.

But the NDP and Liberal leaders were consulted ahead of time when Porter was first appointed and raised no objections, countered Public Safety Minister Vic Toews.

Under the government security policy, there are three levels of security clearance — confidential, secret and top secret.

According to CSIS, top secret clearances require a full field investigation, which involves checking the intelligence service's records, interviewing friends, neighbours and employers, consulting with local police and possibly interviewing the applicant.

Under the new process, CSIS looks into the background of prospective review committee members and provides an assessment to the Prime Minister's Office. The prime minister then decides whether to go ahead with the appointment.

It is the same security-clearance process that is applied to Ottawa-based staff members who support the work of the intelligence review committee.

But before the Porter affair, political appointees to the review committee underwent a less thorough vetting, say those with knowledge of the process.

"I was not security-cleared at the time I was appointed," said Ron Atkey, who served as intelligence review committee chairman from 1984-89.

Atkey, a lawyer and former cabinet minister, did later go through the top-secret security clearance process upon being appointed to a special role with the federal inquiry into Ottawa engineer Maher Arar's imprisonment and torture in Syria.

He underwent another top-level clearance upon becoming a special advocate in court cases involving national security matters.

"But strangely enough, when I was chair of SIRC, I was not," Atkey said. "So it is an anomaly, and practice is catching up with what it should be."

As political appointees, prospective review committee members have long been vetted — at least to some degree — by the Prime Minister's Office. Parties with official standing in the House of Commons have traditionally been consulted on nominees, as Toews indicated Thursday, and the makeup of the committee has generally reflected the breadth of the political spectrum.

In addition, review committee members have always become privy councillors — if they were not already — meaning they must swear an oath of allegiance to the Queen and promise to keep confidential matters secret.

But the new security screening procedures go much further.

Had a full, top-secret clearance check been done on Porter, "the prime minister might not have appointed him," Atkey said.

Raymond Rivet, a spokesman for the Privy Council Office, refused to discuss the previous vetting protocol for intelligence review committee appointees.

"There was a security clearance procedure in place but I have no additional information to provide on this."

Dave Penner, director of appointments in the Prime Minister's Office when Porter was named to the review committee, declined to comment.

However, Rivet provided a full explanation of the new process, saying the Privy Council Office "ensures the continued loyalty and reliability of personnel through the cycle of security clearance and background check updates."

"A person's foreign connections are considered on a case-by-case basis during the security clearance process," he added.

In addition, a security clearance may be suspended or revoked if information is uncovered that raises serious concerns about an individual's reliability or loyalty, Rivet said.

Andrew MacDougall, a spokesman for the Prime Minister's Office, said the government "has taken steps to strengthen the review process."

The fact that CSIS now examines the background of pending review committee appointees might raise the question of whether it's appropriate for the spy service to have a hand in vetting people chosen to look over its shoulder.

However, MacDougall said "the organization doing the vetting is not told what position the candidate is being considered for, only that a screening is to be done."

Atkey said there is nothing to be concerned about, noting CSIS is limited to gathering facts about a prospective appointee.

"They can't present false facts to the Prime Minister's Office," he said. "And if the prime minister wants to appoint somebody even though they've got negative information (collected by CSIS), that really falls on the prime minister's shoulders."